Vehicle control system

ABSTRACT

A Brake Traction Control System (BTCS) for an off-road type vehicle includes a 2WD/4WD switch adapted to switch a drive mode of the vehicle between a two-wheel drive mode (2WD) and a four-wheel drive mode (4WD). The switch is configured to be manually activated by an associated vehicle operator. A control unit is in signal communication with the 2WD/4WD switch. The control unit is operable to activate the BTCS only if the drive mode is switched to the four-wheel drive mode and predetermined vehicle operating conditions relating to engine throttle position or opening and wheel speed are subsequently satisfied.

BACKGROUND

A variety of control systems are provided on a vehicle for control ofdrive configurations or characteristics of the vehicle. One such controlsystem is a hill start assist (HSA) system. As is well know, the HSAsystem automatically maintains a vehicle brake when the vehicle islocated on a hill as the vehicle is traveling below some predeterminedminimum speed value. Typical HSA systems will maintain the vehiclestationary while the vehicle is on a grade to permit the vehicleoperator to start the vehicle in a desired direction of travel whilepreventing the vehicle from rolling in the opposite direction. Many HSAsystems include a variety of inputs for actuating and deactivating thesystem (e.g., lateral and longitudinal acceleration sensors fordetecting vehicle speed and vehicle position angle). Another type ofvehicle control system is a brake traction control system (BTCS). Thiscontrol system controls driving force distribution between wheelsaccording to driving conditions of the vehicle.

Control of drive configurations or characteristics of off-road typevehicle (e.g., all-terrain vehicle, multi-utility vehicle, side-by-sidevehicle and other types of like utility vehicles) can be unique to suchvehicles. Such vehicles are often capable of being driven over uneven orhilly terrains, and therefore the known HSA systems that areautomatically operable based on sensed vehicle position angle can limitHSA usability in off-road conditions. Such vehicles are also oftencapable of encountering soft, loose or slippery soils as well as snowand/or ice and optimum drive characteristics can vary from rear wheeldrive (where only the rear wheels provide traction), front and rearwheel drive (sometime referred to as four wheel drive where the rearwheels and at least one of the front wheels provide traction), and allwheel drive (where the rear wheels and both front wheels providetraction). In some known off-road type vehicles, the operator canmanually select the drive configuration (e.g., from rear wheel drive tofour wheel drive) which in turn can impact driving force distributionbetween the front wheels and the rear wheels when terrain surfacefriction is different between the front and rear wheels.

BRIEF DESCRIPTION

In accordance with one aspect, a brake traction control system (BTCS)for an off-road type vehicle operable in one of a two-wheel drive mode(2WD) and a four-wheel drive mode (4WD) comprises a 2WD/4WD switchadapted to switch a drive mode of the vehicle between a two-wheel drivemode (2WD) and a four-wheel drive mode (4WD). The switch is configuredto be manually activated by an associated vehicle operator. A controlunit is in signal communication with the 2WD/4WD switch. The controlunit is operable to activate the BTCS only if the drive mode is switchedto the four-wheel drive mode and predetermined vehicle operatingconditions relating to engine throttle position or opening and wheelspeed are subsequently satisfied.

In accordance with another aspect, a method for selectively activatingand controlling a Brake Traction Control System (BTCS) for an off-roadtype vehicle operable in one of a two-wheel drive mode (2WD) and afour-wheel drive mode (4WD) comprises providing a manually operable2WD/4WD switch having a first state for front-wheel drive (2WD) mode anda second state for four-wheel drive (4WD) mode and determining whetherthe 2WD/4WD switch is in the second state for four-wheel drive (4WD)mode. Wherein only if the vehicle is in the four-wheel drive (4WD) mode,the method further comprises detecting throttle position or opening ofan engine, and comparing the detected throttle position or opening witha predetermined throttle position or opening; calculating wheel speedfor each of left wheels and right wheels, and comparing wheel speedbetween the left wheels and the right wheels; and activating the BTCSonly if the detected throttle position or opening is greater than orequal to the predetermined throttle position or opening and a wheelspeed delta between the left wheels and right wheels is greater than atarget wheel speed delta setting for the vehicle.

In accordance with yet another aspect, an off-road type vehicle operablein one of a two-wheel drive mode (2WD) and a four-wheel drive mode (4WD)comprises an engine and a drive line for transferring a driving force ofthe engine to left and right front wheels via a front differential andto left and right rear wheels via a rear differential. A manual 2WD/4WDswitch is adapted to switch a drive mode of the vehicle between atwo-wheel drive mode (2WD) and a four-wheel drive mode (4WD). A controlunit is configured to control the driving force distributed to the rearwheels by selectively engaging or connecting the rear differential. Thecontrol unit is in communication with the 2WD/4WD switch such that whenthe switch is manually actuated to switch the drive mode to thefour-wheel drive mode (4WD) the rear differential is engaged and enginetorque is distributed to both the front wheels and the rear wheels. Thecontrol unit includes a Brake Traction Control System (BTCS) that isselectively activated only if the drive mode is manually switched to thefour-wheel drive mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an off-road type vehicle includingexemplary vehicle control systems according to the present disclosure.

FIG. 2 is a flow diagram of an exemplary brake traction control for thevehicle of FIG. 1.

FIG. 3 is a state diagram of an exemplary Hill Start Assist (HSA) systemfor the vehicle of FIG. 1.

DETAILED DESCRIPTION

It should, of course, be understood that the description and drawingsherein are merely illustrative and that various modifications andchanges can be envisioned without departing from the present disclosure.For purposes of understanding, the term “signal” utilized herein isdefined as any electrical signal or any stored or transmitted value. Forexample, a signal can comprise a voltage, or a current. Further, asignal can comprise any stored or transmitted value such as binaryvalues, scalar values, or the like. Moreover, the term “approximately”as used herein means a reasonable amount of deviation of the modifiedword is contemplated such that the end result is not significantlychanged. For example, such term can be construed as allowing a deviationof at least 5% of the modified word if this deviation would not negatethe meaning of the word this term of degree modifies. It will also beappreciated that the various identified components of the exemplaryvehicle control systems disclosed herein are merely terms of art thatmay vary from one manufacturer to another and should not be deemed tolimit the present disclosure.

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings. As schematicallyillustrated in FIG. 1, an off-road type vehicle 100 (e.g., all-terrainvehicle, multi-utility vehicle, side-by-side vehicle and other types oflike utility vehicles) includes an engine 102 and a transmission (notshown) (e.g., an automatic transmission) disposed with the engine. Adrive line 110 (e.g., a propeller shaft) transfers a driving force ofthe engine to front wheels W1 and W2 via a front differential 112 whichdistributes the driving force to left and right front drive shafts 114and 116, and to rear wheels W3 and W4 via a rear differential 120 whichdistributes the driving force to left and right rear drive shafts 122and 124. As is well known, a vehicle controller 140 can control thedriving force distributed to the rear wheels W3 and W4 by selectivelyengaging or connecting the rear differential 120 so that the frontwheels W1 and W2 serve as primary drive wheels and the rear wheels W3and W4 serve as secondary drive wheels. That is, if the reardifferential 120 is disengaged (disconnected), the driving force of thedrive line 110 is not transferred to the rear differential 120 and,thus, the entire torque of the engine 102 is transferred to the frontwheels W1 and W2. Accordingly, the vehicle is driven in a front-wheeldrive mode (a 2WD mode). In contrast, if the rear differential 120 isengaged (connected), the driving force of the drive line 110 istransferred to the rear differential 120 and, thus, the torque of theengine is distributed to the front wheels W1 and W2 and the rear wheelsW3 and W4. Accordingly, the vehicle 100 is driven in a four-wheel drivemode (a 4WD mode).

It should be appreciated that the exemplary off-road type vehicle 100can travel while arbitrarily making the switch between front-wheel drivemode and four-wheel drive mode. By way of example, a 2WD/4WD switch 144can be provided on a vehicle instrument panel (not shown) at a positionwhere it can easily be operated by the vehicle operator. The vehiclecontroller 140 is in signal communication with the 2WD/4WD switch 144,such that when the 2WD/4WD switch 144 is manually actuated by thevehicle operator the rear differential 120 is engaged and, thus, thetorque of the engine 102 is distributed to both the front wheels W1 andW2 and the rear wheels W3 and W4.

The vehicle 100 further includes a FI/AT (Fuel Injected/AutomaticTransmission)-ECU (Electronic Control Unit) 150 and a VSA (VehicleStability Assist)-ECU 152, each being in communication with the otherand the vehicle controller 140. As is well known, the FI/AT-ECU 150serves as a control unit that controls the engine 102 and the automatictransmission. The FI/AT-ECU 150 can receives a detection signal of athrottle position or throttle opening detected by a throttle positionsensor 156, a detection signal of an engine speed detected by an enginespeed sensor (not shown), and a detection signal of a shift positiondetected by a shift position sensor (not shown). In addition, theFI/AT-ECU 150 can have an engine torque map that describes arelationship among the engine speed, the throttle position, and anengine torque estimation value. According to this aspect, the FI/AT-ECU150 can calculate the engine torque estimation value on the basis of thethrottle position detected by the throttle position sensor 156 and theengine speed detected by the engine speed sensor.

The VSA-ECU 152 is a control unit that has a BTCS (Brake TractionControl System) function that prevents tire slip in acceleration. Withthe BTCS of the exemplary off-road type vehicle 100, when terrainsurface friction is different for the left and right wheels, brakecontrol is applied to the wheel(s) on the low friction side while enginetorque is supplied to the wheel(s) on the high-friction side, thusobtaining all wheel traction. The VSA-ECU 152 can also have an ABS(Anti-lock Braking System) function that prevents wheel lock byperforming anti-lock control on the left and right front wheels W1 andW2 and the left and right rear wheels W3 and W4 when braking is applied.By controlling these functions, the VSA-ECU 152 can improve thestability characteristics of the vehicle 100.

Still further, the off-road type vehicle 100 includes a left front wheelspeed sensor 170 that detects the wheel speed of the left front wheel W1on the basis of the rotational speed of the left front drive shaft 114,a right front wheel speed sensor 172 that detects the wheel speed of theright front wheel W2 on the basis of the rotational speed of the rightfront drive shaft 116, a left rear wheel speed sensor 174 that detectsthe wheel speed of the left rear wheel W3 on the basis of the rotationalspeed of the left rear drive shaft 122, and a right rear wheel speedsensor 176 that detects the wheel speed of the right rear wheel W4 onthe basis of the rotational speed of the right rear drive shaft 124. Thefour wheel speed sensors 170, 172, 174, 176 are in signal communicationwith the vehicle controller 140 and, in turn, each of the FI/AT-ECU 150and VSA-ECU 152.

As indicated previously, the 2WD/4WD switch 144 is operably associatedwith the vehicle controller 140 allowing the vehicle operator toselectively switch between front-wheel drive (2WD) mode and four-wheeldrive (4WD) mode. According to the present disclosure, the BTCS of theVSA-ECU 152 is only activated when the vehicle is in the 4WD mode. Moreparticularly, when the vehicle 100 is in 2WD drive mode, the BTCS isinactive and brake control as described above is not applied to the leftand right wheels. At Step S200 of FIG. 2, the state of 2WD/4WD switch144 is determined by the vehicle controller 140. Upon the vehicleoperator manually switching to 4WD mode via the 2WD/4WD switch 144(i.e., 4WD mode is engaged), the VSA-ECU 152 continuously monitorscertain conditions of the vehicle 100 at Step S202 prior to activatingBTCS. According to one embodiment, the VSA-ECU 152 receives enginethrottle position or opening information via serial communication withthe FI/AT-ECU 150. The VSA-ECU 152 also receives detection signalsoutput from the wheel speed sensors 170, 172, 174, 176, and wheel speedfor each of the wheels W1, W2, W3, W4 is calculated. At Step S202 ofFIG. 2, and upon the 4WD mode being engaged, the VSA-ECU 152 determineswhether the throttle position or opening (as detected by the throttleposition sensor 156) is greater than or equal to a predeterminedthrottle position or opening. According to one aspect, the predeterminedthrottle position or opening is approximately one (1) degree. At StepS202 the VSA-ECU 152 also compares the wheel speed between the leftwheels W1, W3 and the right wheels W2, W4, and whether a wheel speeddelta between of the left and right wheels is greater than a targetwheel speed delta setting for the vehicle 100, which can be provided ina look-up table of the VSA-ECU 152.

If it is determined at Step S202 of FIG. 2 that in the 4WD mode thethrottle position or opening is greater than or equal to thepredetermined throttle position or opening (e.g., approximately onedegree) and the wheel speed delta between of the left and right wheelsis greater than the target setting, the VSA-ECU 152 activates the BTCS.While the BTCS is active the VSA-ECU 152 continuously monitors theswitch state, the throttle position or opening and the wheel speeddelta. At Step S202 of FIG. 2, if the throttle position or opening asdetected by the throttle position sensor 156 becomes less than thepredetermined throttle position or opening (e.g., approximately onedegree), the BTCS is inactive. Further, at Step S202, if the wheel speeddelta becomes less than the target setting, the BTCS is inactive.Therefore, only when the 4WD mode is engaged and if both the throttleposition and wheel speed delta conditions are met will the BTCS beactivated by the VSA-ECU 152. Once so activated, the VSA-ECU 152continuously monitors the throttle position or opening and wheel speeddelta. If either of the throttle position or opening or the wheel speeddelta falls below its respective predetermined threshold for theoff-road type vehicle 100 and/or if the switch state changes back to 2WDmode, the VSA-ECU 152 deactivates the BTCS.

It should be appreciated from the foregoing that a method forselectively activating and controlling the BTCS of the VSA-ECU 152 forthe off-road type vehicle 100 comprises providing the manually operable2WD/4WD switch 144 having a first state for rear-wheel drive (2WD) modeand a second state for four-wheel drive (4WD) mode and determiningwhether the 2WD/4WD switch 144 is in the second state for four-wheeldrive (4WD) mode. Wherein only if the vehicle 100 is in the four-wheeldrive (4WD) mode, the method further comprises detecting throttleposition or opening of the engine 102, and comparing the detectedthrottle position or opening with a predetermined throttle position oropening; calculating wheel speed for each of left wheels and rightwheels, and comparing wheel speed between the left wheels and the rightwheels; and activating the BTCS of the VSA-ECU 152 only if the detectedthrottle position or opening is greater than or equal to thepredetermined throttle position or opening and a wheel speed deltabetween the left wheels and right wheels is greater than a target wheelspeed delta setting for the vehicle 100.

While the BTCS of the VSA-ECU 152 is activated, the exemplary methodfurther includes continuously monitoring the switch state anddeactivating the BTCS if the 2WD/4WD switch 144 is moved back to thefirst state; and/or continuously monitoring the throttle position oropening and deactivating the BTCS if the detected throttle position oropening is less than the predetermined throttle position or opening;and/or continuously monitoring the wheel speed delta between the leftwheels and right wheels and deactivating the BTCS if the wheel speeddelta is less than the target wheel speed delta setting for the vehicle.

With reference back to FIG. 1, the off-road type vehicle 100 is furtherprovided with a brake system including front wheel brakes 180, 182 forthe respective left and right front wheels W1, W2 and rear wheel brakes184, 186 for the respective left and right rear wheels W3, W4. The brakesystem further includes a brake modulator 188 (e.g., a brake control orregulatory valve), a manual brake switch or actuator 190 (i.e., brakepedal), a brake sensor 192, a brake light switch 194, and a master brakecylinder 196 (which is operably connected to the brake modulator 188).The brake sensor 192 is adapted to provide a signal indicating whetherthe front and rear vehicle brakes are in an engaged or disengagedcondition (i.e., whether the manual brake actuator 190 is actuated orreleased) and is further adapted to provide a signal indicative of amaster brake cylinder pressure. As is well known, the brake light switch194 is an electrically powered switch that triggers brake lights toactivate when the brakes are applied. The front and rear wheel brakes180, 182, 184, 186 are operated by pressurized fluid such as air or asuitable brake fluid that is conveyed under pressure from the masterbrake cylinder 196 to respective wheel brake cylinders (not shown) thatare mechanically linked to the brakes and operative to move the brakesinto engagement when pressurized as is well known to those skilled inthe art of vehicle brakes.

The brake system of the vehicle 100 can be controlled by the vehiclecontroller 140 and can receive detection signals output from the varioussensors in signal communication with the respective FI/AT ECU 150 andVSA-ECU 152. The vehicle controller 140 is provided with a HSA (HillStart Assist) system 210 for maintaining the off-road type vehicle 100stationary (via, for example, front and rear wheel brakes 180, 182, 184,186) while the vehicle is on a grade to permit the vehicle operator tostart the vehicle in a desired direction of travel while preventing thevehicle from rolling in the opposite direction. In the embodimentillustrated in FIG. 1, the HSA system 210 is a manually operated systemthat can be selectively activated by the vehicle operator via a HSAswitch 212, which can be located on the instrument panel, in addition toother vehicle operating conditions that have to be satisfied. Furtherassociated with the present HSA system 210 are the wheel speed sensors170, 172, 174, 176 and an acceleration pedal sensor 216 for detectingangular displacement of an acceleration switch or actuator 218 (i.e.,acceleration pedal). As depicted, the detection signals output from thewheel speed sensors are sent to the vehicle controller 140.

FIG. 3 depicts the various operational states of the exemplary HSAsystem 210, which are labeled for ease of description only. In the “HSANot Ready” (i.e., deactivated) state, the brake modulator (i.e., brakecontrol or regulation valve) 188 is open and an HSA “Hill” indicator 230located on the instrument panel is not illuminated or off. At 300, theHSA system 210 moves to the “HSA Ready” state only when certain vehicleconditions associated with the HSA system 210 have been satisfied.Specifically, the HSA system 210 moves from the “HSA Not Ready” state tothe “HSA Ready” state when the vehicle controller 140 confirms each of(1) the vehicle is stopped, (2) the manual brake actuator 190 isengaged, (3) the acceleration pedal 218 is released, (4) the HSA switch212 has been manually activated by the vehicle operator (e.g. the HSAswitch 212 is depressed by the vehicle operator for a predetermined timeperiod), and (5) the brake light switch 194 is activated or on.

More particularly, the vehicle controller 140 receives detection signalsoutput from the wheel speed sensors 170, 172, 174, 176 (and/or vehiclespeed sensor 220), and verifies that wheel speed for each of the wheelsW1, W2, W3, W4 is approximately equal to 0 km/h (i.e., that the vehicle100 is stopped or not moving for a predetermined time period). Thevehicle controller 140 receives detection signals from the brake sensor192 that are indicative of one of an angular displacement of the manualbrake actuator 190 (i.e., brake pedal) and pressure of the master brakecylinder 196. According to one aspect, the vehicle controller 140receives a signal from the brake sensor 192 that pressure of the masterbrake cylinder 196 is greater than a defined pressure amount. Thevehicle controller 140 further receives detection signals from the pedalsensor 216 that angular displacement of the acceleration pedal 218 isless than a defined angle amount. Further, the vehicle controller 140verifies that the HSA switch 212 and a brake light switch 194 are on.According to another aspect, and as a further requirement of the “HSAReady” state, the vehicle controller 140 determines that each of theabove conditions have been met for a time period greater than apredetermined time.

It should be appreciated that while in the “HSA Ready” state, thevehicle controller 140 continues to monitor the vehicle conditionsdescribed above. And at 302 of FIG. 3, if the vehicle controller 140receives a signal from (1) the wheel speed sensors 170, 172, 174, 176that wheel speed for the wheels W1, W2, W3, W4 is greater than 0 km/h(i.e., that the vehicle 100 is moving), (2) the pedal sensor 216 thatangular displacement of the acceleration pedal 218 is greater thanapproximately zero degrees, and/or (3) the HSA switch 212 is againactivated by the vehicle operator after being released once, the HSAsystem 210 moves back to the “HSA Not Ready” state.

In the “HSA Ready” state, the brake modulator 188 is open and the HSA“Hill” indicator 230 is illuminated or on. At 304, the HSA system 210moves to the “HSA Activated” state when the vehicle controller 140confirms that the condition of the manual brake actuator 190 (i.e.,brake pedal) described above remains. In the “HSA Activated” state thebrake modulator 188 is closed and master brake cylinder pressure beginsto release. And the HSA “Hill” indicator 230 remains illuminated or on.

At 306 of FIG. 3, the HSA system 210 moves from the “HSA Activated”state to the “HSA Hold” state. The vehicle controller 140 receivesdetection signals from the brake sensor 192 that the manual brakeactuator 190 is released and/or pressure of the master brake cylinder196 is less than or equal to the defined pressure amount. Alternatively,at 306 of FIG. 3 the vehicle controller 140 determines that the brakelight switch 194 is not activated or off. If one of these conditions isdetermined by the vehicle controller 140, the HSA system 210 moves tothe “HSA Hold” state, wherein the brake modulator 188 remains closed anda start hold timer begins for a defined period of time. Further, in the“HSA Hold” state of the HSA system 210 the HSA “Hill” indicator 230flashes for the period of the start hold timer.

It should be appreciated that the vehicle controller 140 continues tomonitor the vehicle conditions required for the “HSA Hold” state of theHSA system 210. In the event that at 308 of FIG. 3 the vehiclecontroller 140 receives detection signals from the brake sensor 192 thatthe manual brake actuator 190 is again pressed and/or pressure of themaster brake cylinder 196 is greater than the defined hold pressure orthat the brake light switch 194 is again activated or on, the HSA system210 moves to a “HSA Reset Hold” state. While in the “HSA Reset Hold”state, the vehicle controller 140 continues to monitor the vehicleconditions described above. And at 310 of FIG. 3, if the vehiclecontroller 140 determines that the conditions for transitioning from the“HSA Activated” state to the “HSA Hold” state described at 306 are againsatisfied, the HSA system 210 moves back to the “HSA Hold” state.

At 312 of FIG. 3, the HSA system 210 begins to transition from the “HSAHold” state to its “HSA Change to Not Ready” state, which slowlydecreases brake caliper pressure by control of the brake modulator 188(e.g., brake control or regulatory valve). This transition occurs whenthe vehicle controller 140 receives a signal from (1) the pedal sensor216 that angular displacement of the acceleration pedal 218 is greaterthan the defined angle amount, (2) the HSA switch 212 is again activatedby the vehicle operator after being released once, and/or (3) the timeperiod of the start hold timer elapsed. It should also be appreciatedthat the HSA system 210 can move from the “HSA Activated” state to the“HSA Change to Not Ready” state upon determination by the vehiclecontroller 140 of these same vehicle conditions (at 314 of FIG. 3).Finally, at 316 of FIG. 3, the HSA system 210 moves back to the “HSA NotReady” state and the brake modulator 188 is opened completely.

Therefore, as is evident from the foregoing description of the exemplaryHSA system 210 for the off-road type vehicle 100, if the vehicleoperator requests a HSA operation to hold the vehicle 100 on anincline/decline, the HSA system 210 holds brake pressure in order toprevent the vehicle from moving. The HSA system 200 generally controlsthe brake pressure for a predetermined period of time after the vehicleoperator applies HSA switch 212 and has released the manual brakeactuator 190, or until the accelerator pedal 218 is applied. It shouldbe appreciated that the vehicle operator can stop operation of the HSAsystem 210 at any time by again depressing the HSA switch 212.Accordingly, there is provided a variety of inputs for actuating anddeactivating the exemplary HSA system 210, none of which are sensors fordetecting vehicle position angle or slope. In other words, the HSAsystem 210 is operable without regard to position angle or slopesensors.

FIG. 3 depicts illumination of the HSA “Hill” indicator 230 duringoperation of the HSA system 210, particularly at the identified statesof the HSA system 210. In FIG. 3, the HSA “Hill” indicator 230 is in theon condition in the “HSA Ready” state until brake pressure is released,and is in the intermittent on condition in the “HSA Hold” state.Therefore, the present disclosure provides an indication signal that isilluminated when the HSA system 210 is ready and activated (as describedin detail above) and then flashes when the vehicle 100 is being held bythe HSA system 210.

As is evident from the foregoing, an exemplary method of controlling theHSA system 210 for the off-road type vehicle 100 is provided. The methodgenerally comprises controlling a brake modulator of a brake system tomaintain a braking force sufficient to maintain the vehicle 100 in astopped condition when a manual brake actuator of the brake system is ina released position; transitioning the HSA system 210 from a deactivatedstate to a ready state by determining that the vehicle is in the stoppedcondition, the manual brake actuator is in an engaged position, anacceleration pedal is in a released position, and a HSA switch 212 ismanually activated by an associated vehicle operator; transitioning theHSA system 210 from the ready state to an activated state where thebrake modulator is in a closed condition and the braking force ismaintained; transitioning the HSA system 210 from the activated state toa hold state where the brake modulator remains in the closed position bydetermining that the manual brake actuator is in the released position;and transitioning the HSA system 210 from the hold state back to thedeactivated state.

As described in detail above, transitioning the HSA system 210 from theactivated state to a hold state is based on determining the manual brakeactuator is in the released position. The exemplary method furthercomprises transitioning the HSA system 210 from the hold state to theactivated state is based on determining the manual brake actuator is inthe engaged position; transitioning the HSA system 210 from any one ofthe ready, activated and hold states to the deactivated state based ondetermining one of the HSA switch 212 is again activated by theassociated vehicle driver, the vehicle not being in the stopped and theacceleration pedal is in a depressed position; and transitioning the HSAsystem 210 from any one of the activated state and the hold state to thedeactivated state based on determining that a time period is expired.

It should be appreciated that any suitable controller and/or electroniccontrol unit which acts to receive the desired inputs and calculate thedesired outputs may be employed for the vehicle controller 140, FI/ATECU 150 and VSA-ECU 152. It should be further appreciated by one skilledin the vehicle control arts that each of the vehicle controller 140,FI/AT ECU 150 and VSA-ECU 152 can be formed from a microcomputer orprocessor including a random access memory (RAM), a read only memory(ROM), a central processing unit (CPU), and an I/O interface (none areillustrated), wherein the controller and ECUs execute softwareimplemented functions to control operation of the vehicle 100. It shouldbe further appreciated that although each of the vehicle controller 140,FI/AT ECU 150 and VSA-ECU 152 are depicted as separate control units,each can be selectively integrated into a single controller or controlunit. Still further, insofar as each of the vehicle controller 140,FI/AT ECU 150 and VSA-ECU 152 is disclosed as a singular microcomputeror processor it is to be appreciated that each may be composed ofseveral processors or controllers. Further still, it is also to beappreciated that each of the vehicle controller 140, FI/AT ECU 150 andVSA-ECU 152 may include various other modules or components configuredto perform other vehicle control related functions.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

What is claimed is:
 1. A Brake Traction Control System (BTCS) for anoff-road type vehicle operable in one of a two-wheel drive mode (2WD)and a four-wheel drive mode (4WD) comprising: a 2WD/4WD switch adaptedto switch a drive mode of the vehicle between a two-wheel drive mode(2WD) and a four-wheel drive mode (4WD), the switch configured to bemanually activated by an associated vehicle operator; and a control unitin signal communication with the 2WD/4WD switch, the control unitoperable to activate the BTCS only if the drive mode is switched to thefour-wheel drive mode and predetermined vehicle operating conditionsrelating to engine throttle position or opening and wheel speed aresubsequently satisfied.
 2. The system of claim 1, where in the controlunit is in signal communication with a throttle position sensor fordetecting engine throttle position or opening and with left and rightwheel speed sensors for detecting wheel speed for left wheels and rightwheels, wherein in the four-wheel drive mode the control unit isoperable to activate the BTCS only if the detected throttle position oropening is greater than or equal to a predetermined throttle position oropening and a wheel speed delta between the left wheels and right wheelsis greater than a target wheel speed delta setting for the vehicle. 3.The system of claim 2, wherein in the four-wheel drive mode the controlunit is operable to deactivate the BTCS if the detected throttleposition or opening is less than the predetermined throttle position oropening.
 4. The system of claim 3, wherein the predetermined throttleposition or opening is approximately one degree.
 5. The system of claim2, wherein in the four-wheel drive mode the control unit is operable todeactivate the BTCS if the wheel speed delta between the left wheels andright wheels is greater than the target wheel speed delta setting forthe vehicle.
 6. The system of claim 5, wherein the target wheel speeddelta for the vehicle is provided in a look up table of the controlunit.
 7. The system of claim 2, wherein in the four-wheel drive mode thecontrol unit is operable to deactivate the BTCS if the drive mode ismanually switched back to the two-wheel drive mode via the 2WD/4WDswitch.
 8. A method of controlling a Brake Traction Control System(BTCS) for an off-road type vehicle operable in one of a two-wheel drivemode (2WD) and a four-wheel drive mode (4WD) comprising: providing amanually operable 2WD/4WD switch having a first state for front-wheeldrive (2WD) mode and a second state for four-wheel drive (4WD) mode;determining whether the 2WD/4WD switch is in the second state forfour-wheel drive (4WD) mode, wherein only if the vehicle is in thefour-wheel drive (4WD) mode, the method further comprises: detectingthrottle position or opening of an engine, and comparing the detectedthrottle position or opening with a predetermined throttle position oropening; calculating wheel speed for each of left wheels and rightwheels, and comparing wheel speed between the left wheels and the rightwheels; and activating the BTCS only if the detected throttle positionor opening is greater than or equal to the predetermined throttleposition or opening and a wheel speed delta between the left wheels andright wheels is greater than a target wheel speed delta setting for thevehicle.
 9. The method of claim 8, wherein while the BTCS is activated,further including continuously monitoring the switch state anddeactivating the BTCS if the 2WD/4WD switch is moved back to the firststate.
 10. The method of claim 8, wherein while the BTCS is activated,further including continuously monitoring the throttle position oropening and deactivating the BTCS if the detected throttle position oropening is less than the predetermined throttle position or opening. 11.The method of claim 10, wherein the predetermined throttle position oropening is approximately one degree.
 12. The method of claim 8, whereinwhile the BTCS is activated, further including continuously monitoringthe wheel speed delta between the left wheels and right wheels anddeactivating the BTCS if the wheel speed delta is less than the targetwheel speed delta setting for the vehicle.
 13. The method of claim 8,wherein while the BTCS is activated, further including continuouslymonitoring both the throttle position or opening and the wheel speeddelta between the left wheels and right wheels and deactivating the BTCSif both the detected throttle position or opening is less than thepredetermined throttle position or opening and the wheel speed delta isless than the target wheel speed delta setting for the vehicle.
 14. Anoff-road type vehicle operable in one of a two-wheel drive mode (2WD)and a four-wheel drive mode (4WD) comprising: an engine; a drive linefor transferring a driving force of the engine to left and right frontwheels via a front differential and to left and right rear wheels via arear differential; a manual 2WD/4WD switch adapted to switch a drivemode of the vehicle between a two-wheel drive mode (2WD) and afour-wheel drive mode (4WD); and a control unit configured to controlthe driving force distributed to the rear wheels by selectively engagingor connecting the rear differential, the control unit being incommunication with the 2WD/4WD switch such that when the switch ismanually actuated to switch the drive mode to the four-wheel drive mode(4WD) the rear differential is engaged and engine torque is distributedto both the front wheels and the rear wheels, wherein the control unitincludes a Brake Traction Control System (BTCS) that is selectivelyactivated only if the drive mode is manually switched to the four-wheeldrive mode.
 15. The vehicle of claim 14, wherein the control unit is insignal communication with a throttle position sensor for detectingthrottle position or opening of the engine and with left and right wheelspeed sensors for detecting wheel speed for the left front and rearwheels and right front and rear wheels, wherein in the four-wheel drivemode (4WD) the control unit is operable to activate the BTCS only if thedetected throttle position or opening is greater than or equal to apredetermined throttle position or opening and a wheel speed deltabetween the left front and rear wheels and right front and rear wheelsis greater than a target wheel speed delta setting for the vehicle. 16.The vehicle of claim 15, wherein in the four-wheel drive mode (4WD) thecontrol unit is operable to deactivate the BTCS if at least one of thedetected throttle position or opening is less than the predeterminedthrottle position or opening and the wheel speed delta between the leftwheels and right wheels is greater than the target wheel speed deltasetting for the vehicle.